A fuel cell system may include a fuel supply system to supply fuel (hydrogen) to a fuel cell stack, an air supply system to supply oxygen in the air, serving as an oxidizer necessary for an electrochemical reaction, to the fuel cell stack, a thermal and water management system to control the operating temperature of the fuel cell stack, and the fuel cell stack to generate electric energy through the electrochemical reaction using hydrogen and air.
The fuel cell stack is manufactured with a structure in which several tens to hundreds of unit cells are stacked, and the unit cell includes a polymer electrolyte membrane which may move protons, a cathode and an anode which are catalyst layers applied to both surfaces of the electrolyte membrane so that hydrogen and oxygen may react with the cathode and the anode, gas diffusion layers stacked on the outer surfaces of the cathode and the anode, and bipolar plates stacked on the outer surfaces of the gas diffusion layers to supply the fuel and to discharge water through channels.
After assembly and manufacture of the fuel cell stack having such a configuration, activity of the fuel cell stack in electrochemical reactions is lower at an initial stage of operation and, thus, in order to maximally secure normal initial performance, an activation process of the fuel cell stack should be necessarily carried Out.
Such an activation process is also referred to as pre-conditioning or break-in, and the main object of the activation process is to activate catalytic layers, i.e., the electrode layers of the fuel cell stack, which do not take part in the reaction, and to sufficiently hydrate the electrolyte membrane so as to secure a proton path.
Further, through the activation process, the ElectroChemical Surface Area (ECSA) of a Pt supported on Carbon (Pt/C) electrode including the anode and the cathode of the fuel cell stack may be extended, and ionic conductivity within the electrolyte membrane in the fuel cell stack, for example, a perflurosulfonic acid membrane (PFSA), may be increased. As a result, initial output of the fuel cell stack to generate electricity may be raised.
Further, based on the activation process, by-products produced by thermal decomposition of Nafion added during manufacture of the electrode of the fuel cell stack is discharged through high humidity operation and, thus, a decrease in performance of the fuel cell stack due to mass transfer resistance may be minimized.
Various methods of activating fuel cells have been proposed but, in order to mass-produce fuel cell stacks mounted in fuel cell vehicles, measures to shorten a time taken for activation and to reduce an amount of consumed hydrogen are desirable.
For this purpose, the applicant of the disclosure already filed a method of accelerating activation of a fuel cell stack in which a process of applying high current to the fuel cell stack for a designated time and a process of maintaining shutdown by pumping hydrogen onto a reaction surface of a cathode for a designated time are repeated several times or more so as to shorten an activation time and simultaneously to reduce an amount of hydrogen consumed for activation [Korean Patent Application No. 10-2015-0067893 (filed on May 15, 2015)].
However, in order to mass-produce fuel cell stacks, an activation method which may further shorten an activation time and further reduce an amount of hydrogen consumed for activation is desirable.